Human stem cells are totipotential or pluripotential precursor cells capable of generating a variety of mature human cell lineages. Evidence exists that demonstrates that stem cells can be employed to repopulate many, if not all, tissues and restore physiologic and anatomic functionality.
Many different types of mammalian stem cells have been characterized. See, e.g., Caplan et al., U.S. Pat. No. 5,486,359 (human mesenchymal stem cells); Hu et al., WO 00/73421 (methods of isolation, cryopreservation, and therapeutic use of human amniotic epithelial cells); Beltrami et al., Cell 114(6):763-766 (2003) (cardiac stem cells); Forbes et al., J. Pathol. 197(4):510-518 (2002) (hepatic stem cells). Umbilical cord blood, and total nucleated cells derived from cord blood, have been used in transplants to restore, partially or fully, hematopoietic function in patients who have undergone ablative therapy.
The placenta is a particularly attractive source of stem cells. See, e.g., Hariri, U.S. Patent Application Publication Nos. 2002/0123141 and 2003/0032179. While placentas are readily available, it is desirable to maximize the number of stem cells obtained from each placenta. Stem cells, like other types of cells, are sensitive to environmental changes brought about during collection and storage. These changes can bring about apoptosis or necrosis of the stem cells. There is thus a need for improved compositions and for the collection of placental stem cells from a post-partum mammalian placenta so as to recover increased numbers of stem cells from a single placenta.